Disconnectable heat exchanger

ABSTRACT

The invention is based on a heat exchanger ( 10 ) between a cooling circuit and an exhaust-gas line of an internal combustion engine that comprises a coolant inflow ( 26 ) and a coolant return ( 28 ) for coolant ducts ( 14 ), as well as an exhaust-gas inlet ( 30 ) and an exhaust-gas outlet ( 32 ) for exhaust-air ducts ( 36 ).  
     It is proposed that it is arranged in a main exhaust-gas flow ( 34 ), and that a shutoff device is provided in the coolant inflow ( 26 ).

RELATED ART

[0001] The invention is based on a heat exchanger according to thepreamble of Claim 1.

[0002] The specific contamination of the environment resulting from theemission of carbon dioxide by internal combustion engines is primarily afactor of their efficiency. This is not satisfactory, among otherthings, when the internal combustion engine is operated below itsoptimal operating temperature. In a few operating conditions, such asduring cold starting or long downhill driving of motor vehicles, theoptimal temperature of the internal combustion engine is not reached,which leads to increased fuel consumption and increased exhaust-gasemissions. During cold starting at low outside temperatures, heat isalso needed to deice the windows or to warm the passenger compartment ofthe vehicle, in order to improve driving safety and comfort. Currently,chemical or electrical supplementary heating systems are used inparticular to solve this problem. Their use also results in increasedfuel consumption, however.

[0003] A heat exchanger was made known in a supplement entitled “SystemPartners 98”, page 4 of the MTZ (Motor Technische Zeitschrift) Jul. 2,1998 that is installed in an exhaust-gas return line in order to coolthe exhaust gas to be returned to a combustion chamber of the internalcombustion engine. Cooling the exhaust gas improves the aspiration.Since the heat exchanger is used constantly during the entire operationof the internal combustion engine, heat is continuously absorbed by thecoolant of the internal combustion engine, even during full-loadoperation. In order to prevent overheating of the coolant and theinternal combustion engine in this driving state, however, heat mustalso be dissipated by way of the main radiator of the internalcombustion engine. The main radiator and the cooling fans assigned to itmust be designed accordingly to be larger in size.

ADVANTAGES OF THE INVENTION

[0004] According to the invention, the heat exchanger is arranged in amain exhaust-gas flow, and a shutoff device is provided in the coolantinflow. As a result, the usable heat of the exhaust air can be usedoptimally during cold starting, in order to reach the operatingtemperature of the internal combustion engine as rapidly as possible andto use a sufficient quantity of heat for deicing the vehicle windows,and to warm up the passenger compartment. In his dissertation entitled“Optimization of Fuel Consumption, Emissions, and Heating Comfort inDiesel Vehicles Using Energy Flow Management”, E. D. Pott states thatthe usable heat of the exhaust gas amounts to approximately 1.4 KW injust one driving cycle even in a smaller Diesel internal combustionengine for a passenger car. In a passenger car with an internalcombustion engine that functions according to the Otto principle, theusable heat is markedly greater due to higher exhaust-gas temperatures.

[0005] When the internal combustion engine has reached its optimaloperating temperature, a shutoff valve closes the coolant inflow,thereby interrupting the passage of coolant through the heat exchanger,so that the main radiator of the internal combustion engine and theblower assigned to it do not need to be designed to be larger in size.

[0006] So that the coolant remaining in the heat exchanger when thecoolant inflow is shut off does not overheat and thereby decompose andcause deposits in the coolant ducts of the heat exchanger, it isappropriate to displace the coolant out of the coolant ducts as soon asthe shutoff device in the coolant inflow is closed. The coolant isreturned to the coolant ducts shortly before the shutoff device isreopened. To this end, a gas reservoir is connected at a high point ofthe coolant ducts, from which gas, usually air, is fed into the coolantducts and later removed.

[0007] The gas reservoir is designed in simple fashion as a bellows, onone face of which a connecting line leads to the coolant ducts and onthe opposite face of which an actuator acts. This shortens the bellowsand thereby presses a corresponding volume of gas through the connectingline into the coolant ducts. The actuator can be operated electrically,hydraulically, and/or pneumatically. When the actuator is reset, thebellows expands again and draws the air out of the coolant ducts.

[0008] As an alternative to this, a bypass line is provided between theexhaust-gas inlet and the exhaust-gas outlet, on the branch of which ashutoff device is arranged, in order to control the exhaust-gas inletand the exhaust-gas outlet in complementary fashion. When the shutoffdevice closes the coolant inflow, the shutoff device at the branch ofthe bypass line simultaneously shuts off the exhaust-gas inlet and opensthe bypass line. Since exhaust gas no longer passes through the heatexchanger now, overheating of the coolant is reliably avoided.

[0009] Basically, the heat exchanger can be arranged in any suitablelocation in a main exhaust-gas stream of a vehicle. Appropriately,however, it is arranged behind a catalytic exhaust-gas converter inorder to prevent the catalytic exhaust-gas converter from being delayedin reaching its operating temperature.

DRAWING

[0010] Further advantages arise out of the following drawingdescription. Embodiments of the invention are shown in the drawing. Thedrawing, the description, and the claims contain numerous features incombination. It is appropriate for the expert to also examine thefeatures individually and combine them into additional logicalcombinations.

[0011] The sole FIGURE shows a schematic representation of adisconnectable heat exchanger.

DESCRIPTION OF THE DESIGN EXAMPLES

[0012] The heat exchanger 10 shown functions according to thecountercurrent principle and is arranged in a main exhaust-gas flow 34.It has an exhaust-gas inlet 30 and an exhaust-gas outlet 32 that areconnected with each other by way of exhaust-gas ducts 36. Coolant ducts14, which are connected with a coolant inflow 26 and a coolant return28, are adjacent to the exhaust-gas ducts 36. The coolant flow isindicated by arrows 38 and 40.

[0013] A shutoff device 20 is provided in the coolant inflow 26, whichrestricts or closes the coolant inflow 26 more or less as a function ofthe operating and ambient parameters. The shutoff device 20 iscontrolled by an electronic control device 12 by way of a signal line42. This can be an integrated component of engine electronics.

[0014] The coolant ducts 14 are connected with a gas reservoir 16 by wayof a connecting line 18 at a high point 24, which gas reservoir 16 isdesigned as a bellows and can be changed in its length between lines 52and 54 by way of an actuator. While the connecting line 18 is providedat the one face 48 of the gas reservoir 16, the actuator acts on theopposite face 50. The actuator 22 is also controlled by the electroniccontrol unit 12 by way of a signal line 44.

[0015] When the shutoff device 20 is closed, the actuator 22 begins tofunction and shortens the bellows 16. As a result, the interior space 46of the bellows 16 becomes smaller, so that the gas, usually air, is fedinto the coolant ducts 14 by way of the connecting line 18 and displacesthe coolant there. The coolant can therefore not be heated any furtherby the exhaust gasses.

[0016] Shortly before the shutoff device 20 reopens, the actuator 22returns to its starting position, whereby it draws the gas from thecoolant ducts 14 back into the expanding interior space 46 of thebellows 16. When the passage through the heat exchanger 10 is restored,the coolant can therefore absorb heat from the exhaust air.

[0017] An alternative to this is illustrated using dotted lines. In thisalternative, the exhaust-gas inlet 30 is connected with the exhaust-gasoutlet 32 by way of a bypass line 56. A further shutoff device 58 isprovided in the area of the branch of the bypass line 56, which isconnected with the control unit 12 by way of a signal line 60 andcontrols the exhaust-gas inlet 30 and the bypass line 56 incomplementary fashion, i.e., the exhaust-gas inlet 30 is restricted orclosed that much more, the more the bypass line 56 is opened.

[0018] If the shutoff device 20 at the coolant inflow 26 is now closed,the shutoff device 58 closes the exhaust-gas inlet 30 and opens thebypass line 56 almost simultaneously. The exhaust gas is therebydirected past the heat exchanger 10, so that the coolant in the coolantducts 14 cannot overheat. When the shutoff device 20 opens, the shutoffdevice 58 also opens the exhaust-gas inlet 30 and closes the bypass line56.

[0019] In order to not disrupt the operating behavior of a catalyticexhaust-gas converter, which is not shown in greater detail, it isappropriate to arrange the heat exchanger 10 downstream from thecatalytic exhaust-gas converter.

REFERENCE SYMBOLS

[0020]10 Heatexchanger

[0021]12 Control unit

[0022]14 Coolant duct

[0023]16 Gas reservoir

[0024]18 Connecting line

[0025]20 Shutoff device

[0026]22 Actuator

[0027]24 High point

[0028]26 Coolant inflow

[0029]28 Coolant return

[0030]30 Exhaust-gas inlet

[0031]32 Exhaust-gas outlet

[0032]34 Main exhaust-gas flow

[0033]36 Exhaust-gas duct

[0034]38 Arrow

[0035]40 Arrow

[0036]42 Signal line

[0037]11 Signal line

[0038]46 Interior space

[0039]48 Face

[0040]50 Face

[0041]52 Line

[0042]54 Line

[0043]56 Bypass line

[0044]58 Shutoff device

[0045]60 Signal line

1. Heat exchanger (10) between a cooling circuit and an exhaust-gas lineof an internal combustion engine that comprises a coolant inflow (26)and a coolant return (28) for coolant ducts (14), as well as anexhaust-gas inlet (30) and an exhaust-gas outlet (32) for exhaust-airducts (36), characterized in that it is arranged in a main exhaust-gasflow (34), and that a shutoff device (20) is provided in the coolantinflow (20).
 2. Heat exchanger (10) according to claim 1, characterizedin that a gas reservoir (16) is connected at a high point (24) of thecoolant ducts (14), from which, when the shutoff device (20) is closedand an upper limit temperature of the coolant is reached, gas isdirected from the gas reservoir (16) into the coolant ducts (14) anddisplaces the coolant from the heat exchanger (10), and that the gas isreturned to the gas reservoir (16) shortly before the shutoff device(20) is opened.
 3. Heat exchanger (10) according to claim 2,characterized in that the gas reservoir (16) is designed as a bellows,on one face (48) of which a connecting line (18) is arranged and on theopposite face (50) of which an actuator (22) acts.
 4. Heat exchanger(10) according to claim 3, characterized in that the actuator (22) isoperated electrically, hydraulically and/or pneumatically.
 5. Heatexchanger (10) according to one of the preceding claims, characterizedin that it is arranged in a main exhaust-gas flow (34) in the directionof flow behind a catalytic exhaust-gas converter.
 6. Heat exchanger (10)according to one of the claims 1 or 5, characterized in that, betweenthe exhaust-gas inlet (30) and the exhaust-gas outlet (32), a bypassline (56) is provided, on the branch of which a shutoff device (58) isarranged in order to control the exhaust- gas inlet (30) and the bypassline (56) in complementary fashion.